No this isn't related to the optimization settings. The optimization settings really only affect the discovery portion of the scan and not the assessment portion.
Normally when a script aborts because it takes too long to complete, 6 minutes, its because the target isn't responding in a timely manner. To narrow this down I'd go back to doing a full vulnerability scan but just on a single target. If you still are receiving those errors I'd scan that target with just 10 credentialed checks and look again for those errors.
What type of connection do you have to those targets?
This is probably going to require you to open up a Service Request so we can gather some data.
This scan was against a single Target. I will run only 10 credentialed checks only, as you suggested.
Our connection to this system is Gigabit.
I will open a Service Request.
Thanks for your help.